Its an older Memphis 1000wat amp but the light doesn't come on. I know the connection is live because it runs its sister amp just fine.

check the fuses on the amp?

if fuses are good and you have solid ground/connections it pretty much narrows it down to a blown amp

This.

Check the other amp on the wires you use for your Memphis.. If the other amp powers on, and your Memphis doesn't, RIP Memphis.

Did this. I heard the light was supposed to turn red.

Usually thats if there is a short

Correct.

If the other amp powered up fine, and your memphis didn't.... Chances are it's blown and not shorted.

take off the cover and look for damage.

should be obvious if somethings happened.

First, check your remote setup. If you are using a switch, that may have burned out. if your connections are all good, and you say it is an older amp, just take off the cover and look for any loose or bad connections. Especially look where the internals meet an external connection. The first thing that usually goes is the power or ground connection here.

Step 1:
Make sure the ground is to the CHASSIS of the vehicle, Scraping away all paint from the surface, with a screwdriver or sand paper.

Step 2:
Take a Small wire ( long enough to go from the POWER to the Remote Lead ) and jump it, MEANING:
Take a wire and attach it to the Power Cable and then put it in the remote turn on.

This is only GOOD for testing, if you jump it and leave it that way the AMP will always be on. A switch can be used.
Good Luck